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                            <div style="color:gray; word-break: break-all; font-size:12px;">原英文版地址: <a href="https://www.elastic.co/guide/en/elasticsearch/reference/7.7/mapping-field-meta.html" rel="nofollow" target="_blank">https://www.elastic.co/guide/en/elasticsearch/reference/7.7/mapping-field-meta.html</a>, 原文档版权归 www.elastic.co 所有<br/>本地英文版地址: <a href="../en/mapping-field-meta.html" rel="nofollow" target="_blank">../en/mapping-field-meta.html</a></div>
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<strong>重要</strong>: 此版本不会发布额外的bug修复或文档更新。最新信息请参考 <a href="https://www.elastic.co/guide/en/elasticsearch/reference/current/index.html" rel="nofollow">当前版本文档</a>。
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<span class="breadcrumb-link"><a href="index.html">Elasticsearch Guide [7.7]</a></span>
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<span class="breadcrumb-link"><a href="mapping-params.html">Mapping parameters</a></span>
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<span class="breadcrumb-node"><code class="literal">meta</code></span>
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<a id="mapping-field-meta"></a><code class="literal">meta</code><a class="edit_me edit_me_private" rel="nofollow" title="Editing on GitHub is available to Elastic" href="https://github.com/elastic/elasticsearch/edit/7.7/docs/reference/mapping/params/meta.asciidoc">edit</a>
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<p>Metadata attached to the field. This metadata is opaque to Elasticsearch, it is
only useful for multiple applications that work on the same indices to share
meta information about fields such as units</p>
<div class="pre_wrapper lang-console">
<pre class="programlisting prettyprint lang-console">PUT my_index
{
  "mappings": {
    "properties": {
      "latency": {
        "type": "long",
        "meta": {
          "unit": "ms"
        }
      }
    }
  }
}</pre>
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<p>Field metadata enforces at most 5 entries, that keys have a length that
is less than or equal to 20, and that values are strings whose length is less
than or equal to 50.</p>
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<p>Field metadata is updatable by submitting a mapping update. The metadata
of the update will override the metadata of the existing field.</p>
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